Effect of interleukin-29 on interferon- alpha secretion by peripheral blood mononuclear cells

ABSTRACT

The effect of interleukin [IL]-29, a new therapeutic agent similar to type I interferons [IFNs], on IFN- alpha secretion of human plasmacytoid dendritic cells [pDCs] has not been studied. Therefore, in this study, we aimed to clarify the effect of IL-29 on IFN- alpha secretion of pDCs using human peripheral blood mononuclear cells [PBMCs] in the presence of cytosine-phosphate-guanosinemotif-containing oligodeoxy nucleotides [CpG]. In this experimental and prospective study, PBMCs were obtained from 11 healthy volunteers and divided into four culture conditions I. control, II. CpG treatment, III. IL-29 treatment and IV. CpG plus IL-29 treatment. The amount of IFN- alpha secretion was measured from each culture supernatant by flow cytometry using the flowcytomix apparatus [eBioscience, Vienna, Austria]. Fractional IFN- alpha production of the cultured PBMCs was measured by intracellular staining using the cytomics FC 500 system [Beckman Coulter, Brea, CA, USA] with CXP Software. The mean +/- standard deviation [SD] of supernatant IFN- alpha secretion per pDC/ micro L was 5.7 +/- 9.3 pg/mL/count/ micro L for condition I, 1071.5 +/- 1026.6 pg/mL/count/ micro L for condition II, 14.1 +/- 21.1 pg/mL/count/ micro L for condition III, and 1913.9 +/- 1525.9 pg/mL/count/ micro L for condition IV. There were statistically significant differences between conditions I and II as well as betweenconditions II and IV. Intracellular IFN- alpha production was only detectable in the pDC fraction from one culture; the production amount was similar between the cells treated with CpG and those treated with CpG plus IL-29. Natural killer [NK] cell production of IFN- alpha was observed in two out of three cultures and one culture showed IFN- alpha production in the monocyte fraction. IL-29 alone did not show any effect on IFN- alpha secretion of PBMCs. However, the addition of CpG along with IL-29 enhanced IFN- alpha secretion of PBMCs. Given that pDCs are the major secretors of IFN- alpha in peripheral blood, this result has suggested the possibility that IL-29 has an enhancing effect in human pDC IFN- alpha secretion. Although the supernatant IFN- alpha secretion was not directly correlated with pDCs's intracellular IFN- alpha production in this study, prolonged incubation of pDC and other PB subsets with CpG or IL-29 for over 4 hours could be applied in future studies. These studies would help to elucidate the mechanism of action of IL-29 in human pDCs associated with viral infections